1. Field of the Invention
The present invention relates to image processing apparatuses and methods, recording media, and programs. More specifically, the present invention relates to an image processing apparatus and method, a recording medium, and a program for enhancing sharpness of edges in an image while alleviating noise enhancement.
2. Description of the Related Art
Methods of edge enhancement for enhancing sharpness of edges in an image have hitherto been proposed. However, with existing edge enhancement techniques, in some cases, noise in the vicinity of an edge (e.g., mosquito noise caused by image compression or random noise) is enhanced together with the edge. For example, when a region where the pixel value changes as shown in FIG. 1 exists in an image before edge enhancement, the pixel value changes as shown in FIG. 2 in a corresponding region of an image obtained as a result of edge enhancement using existing techniques. In a region D2a shown in FIG. 2 corresponding to a region D1a shown in FIG. 1, the pixel value changes with a larger gradient than in the region D1a, so that an edge is enhanced. However, in regions in the vicinity of the edge, i.e., in regions D2b and D2c shown in FIG. 2 corresponding to regions D1b and D1c shown in FIG. 1, small fluctuation in the pixel value is amplified.
In a method proposed to avoid degradation in image quality caused by edge enhancement, high-frequency components of an input image are extracted, edges are detected from the high-frequency components, edge frequencies are analyzed, frequencies found by the analysis are modulated, and edge pixels are generated on the basis of the result of the frequency modulation. This serves to enhance edges while alleviating degradation in image quality due to overshoot, undershoot, or the like. Such a method is described, for example, in Japanese Unexamined Patent Application Publication No. 2005-260534.